1. Field of the Invention
This invention relates to opacity measurement devices, and in particular to a smoke or dust density monitor.
2. Background of the Invention
Ships are used extensively in the transportation of goods all over the world. During recent years the ecological impact of these vessels has come under heightened scrutiny. One of the environmental aspects of ship operation are the emissions which emerge from the ship""s funnel, or smokestack. From an environmentally-friendly point of view, it is desirable to minimize smoke emissions from ship smokestacks.
Increasingly, regulations are being passed to encourage reduced ship smokestack emissions. For example, during the year 2000 the state of Alabama is testing a program to monitor ship boiler burner smoke emissions at the smokestack. In the year 2001, smoke emissions monitoring will be required for ships operating in Alabama waters.
Thus it is becoming increasingly important to provide an efficient, accurate apparatus to measure ship burner smoke emissions. Ideally, the smoke monitor should be located on the smokestack itself, and provide alarm and burner shut-down functions if smoke emissions exceed the appropriate thresholds. In addition, a means of providing a record of emissions levels would be desirable.
Existing Designs
One approach to measuring the density of smoke emanating from a ship""s funnel has been to place a twelve volt incandescent light bulb on one side of the funnel, and a photovoltaic cell diametrically opposed on the opposite funnel side. Theoretically, the photo-voltaic cell then emits a voltage signal inversely proportional to the smoke density within the funnel.
A number of problems exist with the incandescent light bulb/photovoltaic cell approach. One problem involves ambient light pollution. Because the photovoltaic cell reacts to all visible light, during bright daylight the voltage out from the photovoltaic cell will be greater than during the night. Thus, ambient light pollution can cause smoke density measurement inaccuracies. It would be desirable to use a smoke detector whose operation is not based on measurements taken in the visible light spectrum.
Another problem with the incandescent light bulb/photovoltaic cell approach involves equipment reliability. A typical twelve-volt incandescent light bulb will burn only 7,000 hours, and then requires replacement. In addition, the type of photovoltaic cell used in this application is generally a selenium cell, which bums out after approximately 10,000 hours. Exacerbating this reliability problem is the physical placement of conventional funnel smoke density measurement light bulbs and photovoltaic cells: they are generally placed high on the smokestack, rendering replacement laborious and difficult. In addition, these elements are typically secured with three or more screws, making replacement quite a chore. It would be desirable to have a slide-in, slide-out installation for easier maintenance.
Still another problem associated with the incandescent light bulb/photovoltaic cell approach is the tendency of the incandescent light bulb to heat up during operation. A hot light bulb attracts dust, which coats the bulb, and reduces its visible light output. This reduction of light output may be interpreted by the photovoltaic cell to be increased smoke density, and lead to measurement errors.
Accordingly, it is an object of the present invention to provide a smoke density monitor which does not operate in the visible light spectrum. Design features allowing this object to be accomplished include a transmitter head which emits infrared light, which in turn is detected by a receiver head. Advantages associated with the accomplishment of this object include elimination of the light pollution associated with incandescent light bulb/photovoltaic cell, and consequently increased smoke density monitor accuracy.
It is another object of the present invention to provide a smoke density monitor which provides increased reliability. Design features allowing this object to be accomplished include a transmitter head and a receiver head connected to a density monitor via fiber-optic lines. Benefits associated with the accomplishment of this object include reduced necessity of maintenance, and hence decreased costs.
It is still another object of this invention to provide a smoke density monitor which is easily maintained. Design features enabling the accomplishment of this object include a transmitter head and receiver head which are easily removed from the smokestack upon which they are mounted. Advantages associated with the realization of this object include easier maintenance, less time required to access the transmitter head and receiver head, and consequently less maintenance cost.
It is another object of the present invention to provide a smoke density monitor which discourages dust from settling on the transmitter and receiver heads. Design features allowing this object to be accomplished include a trap chamber, and a sealing air supply communicating with a head housing exit chamber, which in turn communicates with a smokestack bore through an exit chamber mouth. Benefits associated with the accomplishment of this object include a chamber where particulate matter may be trapped, and also airflow movement away from the transmitter or receiver heads, thereby reducing dust build-up on same, and consequently reduced smoke density measurement errors.
It is yet another object of this invention to provide a smoke density monitor which is relatively inexpensive. Design features allowing this object to be achieved include the use of off-the-shelf components, and the use of components made of readily available materials. Benefits associated with reaching this objective include reduced cost, and hence increased availability.